1. Field of the Invention
This invention relates to a multitrack PCM reproducing apparatus including a reproduced waveform equalizer circuit suitable for integration into an IC.
2. Description of The Prior Art
In the recording onto and reproduction of a digital signal from a magnetic tape, the waveform of the reproduced signal tends to differ or deviate from that of the digital signal being recorded or already recorded on the magnetic tape depending on the transmission characteristics of the magnetic tape and magnetic heads which results in inaccurate transmission of the signal. Especially, in the case of high-density magnetic recording in which an audio signal is recorded on a magnetic tape in a compact cassette with a PCM format, deterioration of the waveform of the reproduced signal is substantial, and it is necessary to apply waveform equalization to the reproduced signal waveform.
FIG. 1 shows the structure of a prior art PCM reproducing apparatus adapted for reproducing PCM signals recorded on a plurality of tracks in a distributed relation. Referring to FIG. 1, PCM signals recorded on a plurality of tracks of a magnetic tape 1 in a distributed fashion are reproduced by associated reproducing heads 2 and then amplified up to a required level by associated amplifier circuits 3. After being subjected to waveform equalization by associated waveform equalizer circuits (analog filters) 4, the PCM signals are converted by associated comparators 5 into digital signals which are applied to a signal processing circuit 6. After being subjected to signal processing including error correction in the signal processing circuit 6, the PCM signals are converted by a D/A converter 7 into analog signals which appear at an audio signal output terminal 8.
FIGS. 2A to 2D show signal waveforms at various parts in FIG. 1. The signal waveform 9 shown in FIG. 2A represents the original waveform of one of the recorded signals before being reproduced by the associated reproducing head 2 in FIG. 1. FIG. 2B illustrates that the output waveform 10 of the amplifier circuit 3 is degrated due to the transmission characteristics of the magnetic tape and magnetic head. Consequently, when such a waveform 10 is converted by the associated comparator 5 into a digital signal by means of zero-point detection, the resultant waveform will be inevitably different from the waveform of the recorded signal, resulting in a data error. Therefore, the amplifier output waveform 10 shown in FIG. 2B is subjected to waveform equalization by the associated waveform equalizer circuit 4 to obtain an equalized waveform 11 as shown in FIG. 2C, and this equalized waveform 11 is then converted by the comparator 5 into a digital signal waveform 12 which is an accurate reproduction of the recorded signal waveform, as shown in FIG. 2D.
An RC filter or a transversal filter is generally used as the waveform equalizer circuit 4. While the RC filter is advantageous in that the circuit size is small and the required equalization characteristic can be easily achieved, it has such a disadvantage that control of the delay characteristic is very long. For the above reason, the transversal filter is preferred for attaining the desired accurate waveform equalization. However, the circuit size of the transversal filter is large, and a multitrack PCM reproducing apparatus requires as many transversal filters as the number of tracks. Thus, great difficulty is encountered in the integration of such a large-scale analog circuit into an IC.